The unique properties of laser radiation, which are related to its monochromaticity, coherence and, in pulsed mode operation, its extremely high intensity, have prompted wide interest in the biological effects of this form of energy. Much of this interest stems from the health hazards associated with laser radiation as well as from the possibility of therapeutic applications in medicine and dentistry. This research is concerned with the understanding of biological laser effects at the molecular level and, more generally, with establishing the utility of the laser as an investigative tool in photochemistry and photobiology. Laser techniques promise to provide some of the finer details of photobiological processes. To implement these aims, the apparatus for laser flash photolysis has been developed and has been used, in conjunction with conventional flash and spectroscopic techniques, to study some model chemical systems. In this project the following specific problems are under investigation by laser techniques: (1) Multiphoton Excitation of biologically significant molecules; (2) flavin photochemistry; (3) mechanisms of photodynamic effects; (4) photochemical and photophysical properties of visual pigments; (5) transient behavior in the solid state.